Technically possible, but not really feasible due to the way Reddit is set up and people who signed up for the app agreed to. It would be a gigantic mess, and I reckon he's not interested in creating a new social platform/link aggregate which is why he would rather refund the ~$250k.
This never struck me as a realistic option. The Apollo user base is orders of magnitude less than Reddit, and, even though Apollo is an incredible iOS app, the primary benefit of a large social network like Reddit is the social network.
Might be a pretty big legal argument if he just copied Reddit backend functionality. Would probably have to redesign the front end from the ground up as well to make it clear it’s not just a rip off.